Process for electrolytic preparation of alkaline-earth alloys



Patented Mar. 15, 1938 1 UNITED STATES PATENT OFFICE PROCESS FOR ELECTROLYTIC PREPARA TION OF ALKALINE-EARTH ALLOYS Robert Andre Gadeau, Saint Jean De Maurienne,

France, assignor' to Chimiques Compagni'e dc Produits et Electrometallurgiques Alais,

Froges et Camargue, Paris, France, a corporation of France No Drawing. ,Application April 18, 1936, Serial No. 75,240. In Germany May 27, 1935 3 Claims.

which contain the corresponding oxide in solu-- tion. The process appears valuable for the prep-.

aration of cerium, but it could never be applied for the preparation of the alkaline earth metals. My experiments have shown'that the electrolysis of a molten bath of calcium chloride, which contains dissolved lime, leads at once to the formation'of a thick slime, which makes the electrolysis as good as impossible. Moreover it is known that the basic chlorides of calcium dissolve metallic calcium, whereby slimy masses are formed and the resistance of the bath is increased. Since the decomposition voltages of calcium oxide and calcium chloride lie close to one another, there takes place, in a molten bath of these two compounds, always in part an electrolysis of the chloride, even if the bath is saturated with lime, which manifests itself in a troublesome evolution of; chlorine and a costly consumption of chloride.

I have found, and'this is the essential char- 3() acteristic of the present invention, that all these difficulties are avoided and that it is possible easily toobtain alkaline earth metals by electrolysis of their oxides, provided that an alkaline earth chloro-fluoride is utilized as oxide-dissolving electrolyte.

My experiments have shown that in an electrolyte, of which the composition corresponds for example to the formula CaCl2.CaFz, the properties of calcium chloride are so far concealed,-

40 that no appreciable volatilization of the bath takes place at about 800, the chloride no longer takes part in the electrolysis and the hath no longer dissolves any appreciable quantity of metallic calcium, whereby the formation of a *slimeof basic subsalts is suppressed.

The process accof'ding to the invention is particularly applicable to the manufacture of alloys of the alkaline earth metals with heavy metals like lead, 'copper, zinc, etc. A bath with bottom made of carbon and walls made of carbon or refractory/ material contains at the bottom the molten eavy-metal, which forms the cathode; the anode is a carbon rod which dips into the electrolyteflconsisting of alkaline earth chloro-fluoride, to which from time to time alkaline earth oxide is-added. The oxide becomes electrolyzed; the alkaline earth metal alloys itself with the heavy metal of the cathode, the oxygen burns away the anode, with evolution of carbon monoxide.

A suitable electrolyte for the preparation of calcium is calcium chloro-fluoride CaClz.CaF2, i. e., a mixture of approximately percent by weight of calcium chloride and 40 percent by' weight of calcium fluoride, in which lime is dissolved. The invention however is not limited to that composition; there is no objection to adding an excess of calcium fluoride. The only limitation is by the rise of the melting point of the mixture, which is at 950 with 50 percent by weight of calcium fluoride. One may also be satisfied with a lower content-of calcium fluoride; I have indeed ascertained that calcium chloride was already stabilized substantially by 10 to 20 percent by weight of calcium fluoride. added periodically, the molte bath is electrolyzed at 6 to 8 volts tension b tween carbon an- .odes and a cathode layer of mo ten lead, which is disposed at the bottom of the bath, wherein the working temperature amounts to about 800". In this waythere is obtained, with a current yield of-' 50 percent, a lead-calcium alloy, in which the calcium is extremely cheap, and which can be utilized as it is for numerous applications.

It is to be quite understood that the invention is not limited to theexample mentioned; in the same way there can be produced various other alloys other than lead-calcium, for example zinccalcium, copper-calcium and so on. I The process is also applicable under the same conditions to the preparation of alloys of barium and of strontium.

Lastly, it is possible to maintain the electrolysis not with an alkaline earth oxide, but with a compound.whicl'rforms the oxide under the in- While lime is fluence of heat, for example with .a carbonate,

oxalate, acetate, and so on. In particular it is of advantage, for example, to prepare calciumfrom calcium carbonate, consequently an extremely cheap mineral.

I have found that pure calcium can be easily,

prepared by electrolytic refining of its heavy alloys which have been obtained according to the present invention. For this the same electrolyte is very well suited; the poles of the bath can therefore be reversed and the carbon electrode replaced for example by a cooled iron cathode, upon which a tube of calcium is then, obtained. I

I have found further that by electrolytic refining of the heavy alloys, prepared according to the present invention, also alloys of aluminium and magnesium with calcium can be easily prepared. It suffices to reverse the poles of the bath and to dispose on the surface of the bath a molten cathode layer of aluminium or magnesium, into which the current is led by a carbon electrode. Electrolysis at a voltage of a few volts causes the calcium of the heavy alloy at the anode to pass into the light alloy at the cathode, with a current yield ofapproximately 100 percent. In the foregoing description and in the claims, there should be understood by the term alkaline earth metals calcium, barium and strontium, to the exclusion of magnesium, the properties of the last differing entirely, from the point of view of electrolysis and the point of view of chemistry from those of calcium, barium and strontium.

What I claim is:

l. A-method of manufacturing an alloy of an alkaline earth metal of the group consisting of calcium, barium and strontium with a heavy metal of the group consisting of lead, zinc and copper, by electrolysis with a carbon anode and a cathode consisting of said fused heavy metal, which comprises dissolving an oxide of said alkaline earth metal in a fused chloro-fluoride of said alkaline earth metal, and electrolyzing the fused bath thus obtained.

2. A method of manufacturing an alloy of an alkaline earth metal of the group consisting of calcium, barium and strontium with a heavy metal of the group consisting of lead, zinc and copper, by electrolysis with a carbon anode and a cathode consisting of said heavy metal in the fused state, which comprises dissolving a carbonate of said alkaline earth metal in a fused chloro-fiuoride of said alkaline earth metal, to give off by the heat of said chloro-fiuorlde the oxide of said alkaline earth metal, and electrolyzing the fused bath thus obtained.

3. A method of manufacturing an alloy of an alkaline earth metal of the group consisting of calcium, barium and strontium with a heavy metal of the group consisting of zinc, lead and copper, by electrolysis with a carbon anode and a cathode consisting of said heavy metal in the fused state, which comprises dissolving lime in a mixture of from 90 to 40 per cent in weight of fused calcium chloride and from 10 to 60 per cent in weight of fused calcium fluoride, and electrolyzing the fused bath thus obtained.

ROBERT ANDRE GADEAU. 

